It has long been desirable to establish a system for supporting and controlling the position, angular orientation, and rotational speed of an object with minimal or without any physical contact to eliminate wear or frictional effect. Such a suspension and control system would have important uses in high-speed rotating devices such as disc drives; however, it also has applicability to robotic joints, the suspension and support of optical elements and other systems where precision of position and orientation control are required.
Conventional mechanical bearings have limitations of limited lifetime, need for lubrication, and performance limitations due to nonlinear frictional characteristics. Hydrodynamic bearings provide a dramatic improvement over such mechanical bearings, but present problems in terms of the needs to maintain the fluid within the bearing gap. Therefore, magnetic bearings have been considered as a solution to these problems.
A number of prior art magnetic bearings have been disclosed, typically utilizing passive methods for restraint. Such passive methods are typically less precise and are very fixed by the initial design, and are therefore less versatile and are inherently limited in their applicability. A number of active magnetic bearings have also been disclosed, including those in U.S. Pat. Nos. 4,000,929 and 4,634,191. The designs disclosed therein, however, comprise a circular stator member cooperating with a suspended annular ring member having radially inward facing pole faces. The flux coils supported on the stator provide variable flux density along radial paths to provide active radial stabilization; flux coils on the stator produce torque moments imposed on the annular ring. However, the entire design is of substantial size and would not lend itself to either small or precisely-controlled systems.